The present invention relates to motor vehicles for cutting grass lawns, and for other agricultural and recreational use; in particular, it relates to suspension systems for four wheeled rotary lawn mowers.
There are a great variety of commercially available machines for mowing lawns and related landscape and agricultural purposes. A popular kind of machine comprises a frame, a wheel at each of the four corners, a rotary mower cutter deck more or less centrally located between the wheels, and an operator seat proximate the rear two wheels. Typically, the two rear wheels are driven to move the mower, and they support the preponderance of the machine and operator weight. Different means are used for steering such vehicles. Preferred is the so-called transmission steer machine, where the mower has two freely pivotable front wheels; and directional control, or steering, is obtained by applying differential power to the two independently driven rear wheels.
Rider mowing machines must give good results for a variety of terrains. It is more difficult in general to mow slopes and undulating surfaces. In particular, when traversing across a slope, there tends to be an imbalance in downward force between the rear wheels, from which directional control can be lost, due to downhill shifting of the line of action of the machine center of gravity. Prior art machines, where the wheels are rigidly mounted at the corners of the vehicle, are particularly prone to this effect. This is because as the machine moves forward, when one front wheel is lifted upward by a small undulation or obstacle, the load at the rear wheel directly behind is lessened. When the front wheel lifted is the uphill wheel, the already low downward force on the uphill rear wheel can become so low that no traction is maintained. As a result, the vehicle will tend to turn and run downhill.
There have been commercial machines in which the front axle is mounted off a center pivot. See for example, U.S. Pat. No. 3,686,840 to Root and U.S. Pat. No. 4,077,191 to Pittinger, Sr. et al. If such design is applied to transmission steerable machines, the above mentioned rear-wheel-lifting effect is avoided.
However, it also a feature of various prior art riding mowing machines that the front wheels will be dropped down from the primary elevation of the axle, whether pivoted or fixed. They will be attached to struts which extend downwardly from the outermost ends of the axle, for the obvious reason of permitting the use of smaller wheels while providing clearance for obstructions or a suspended rotary mower deck. While this configuration serves the intended purpose, when front wheels horizontally hit obstacles, the axle and the pivot point are subjected to very heavy bending moments which can and do cause failure. This necessitates either avoiding the pivot axle type of construction or providing unduly heavy and therefore undesirable pivots and structure.
Thus, there is a need for improved front suspension systems which better maintain contact of wheels with the surface of the earth and enable better control. It is in general a desire to keep overall machine length short, and to keep the center of gravity low; and thus any improvement ought be compatible.
An object of the invention is to provide improved suspension systems for mowing machines and the like. Another object is to provide front wheel suspensions which are articulated to respond to uneven terrain, but which are more durable than prior designs. Another object is to provide improved front wheel suspension system which enables the driver to sit as low as possible on the machine, for stability.
According to the invention a vehicle for mowing grasses and other purposes has a main frame, from which are mounted the rear wheels; and, a subframe, from which are mounted front wheels. The subframe is attached to the front end of the main frame at two longitudinally spaced apart pivots. The main frame is comprised of spaced apart members which define a generally rectangular space sufficient to receive the driver""s feet, located just forward of the driver""s seat which is mounted on the main frame. The subframe is mounted underneath the main frame, so the space for the driver""s feet is not detracted from.
In further accord with the invention, a vehicle for mowing grasses has a main frame with front and rear support members, and spaced apart side members, to define a generally rectangular space. The main frame carries the rear wheels and the cutter deck. A subframe is comprised of front and rear transverse members with side members connecting them to form a generally rectangular subframe. The subframe mounts on the main frame by pivot connections between the respective transverse members and support members. The front wheels rotate about axes which have elevations lower than the elevation of the pivots.
Preferably, the subframe and main frame are of open construction, comprised of welded tubular members. The support and transverse members of the frames are spaced to provide a front to back length, sxe2x80x2, so that the driver""s feet may be accommodated just forward of the driver""s seat which is mounted on the main frame. The lateral width of the space, between the side members of both the subframe and main frame, is also sufficiently wide for the driver""s feet.
Preferably, the subframe cantilevers outwardly from the front end of the main frame by a distance d which is less than about 50% of the pivot to pivot spacing s; the pivot spacing s is more than 40% of the wheel base wb of the vehicle; and, the front wheels rotate about axes having an elevation which is dropped down a distance h from the elevation of the pivots, where h is less than about 50% of s.
Preferably, the invention is part of a transmission steerable vehicle having independent rear wheel suspension. The invention provides a mowing machine with a robust design, while at the same time allowing the front wheels to accommodate small rises and depressions without substantially affecting the cutter deck height.
The foregoing and other objects, features and advantages of the invention will become more apparent from the following description of the best made of the invention and accompanying drawings.